A researcher with the US National Oceanic and Atmospheric Administration surveys a coral reef in the Florida Keys National Marine Sanctuary near Key West, Fla. in this August 2008 file photo. Numerous studies predict corals are headed toward extinction worldwide. Some 50 percent of the Caribbean's corals are already dead, largely because of climate change, overfishing and pollution.

Wilfredo Lee/AP/File

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Miami — The US Army Corps of Engineers on Friday denied a request from researchers seeking more time to save an underwater field of coral in a Miami channel where dredging was set to begin this past weekend.

"Taxpayers would be paying $50,000 to $100,000 a day to keep that dredge on standby and that's not happening," said Susan Jackson, a corps spokeswoman.

The channel is being deepened to 50 feet (15 meters) in the hopes of attracting the larger cargo ships expected to pass through the expanded Panama Canal when it is completed.

Researchers began daily dives to gather coral in and around the dredge site on May 26 after Illinois-based dredging contractor Great Lakes Dredge & Dock finished relocating about 900 more mature corals to an artificial reef as required by the Army Corps of Engineers.

"We've been able to remove more than 2,000 corals in less than two weeks and if we had another two weeks we'd get thousands more," said Colin Foord, a marine biologist and co-founder of Miami-based Coral Morphologic, which is part marine biology lab and part art and music studio.

Though dredging work was scheduled to resume on Saturday, scientists say environmental studies underestimated the number and kinds of corals living near the channel.

"We now have another set of eyes in the water looking at what's down there and we want to be sure what was required in the permit was done," said Rachel Silverstein, executive director of the Biscayne Bay Waterkeepers, which unsuccessfully sued the state in 2011 in hopes of halting the $150 million project.

Coral is a stationary animal that slowly grows on seafloors over tens and even hundreds of years. Foord and scientists at the University of Miami say the corals living in the shallow waters just south of Miami Beach may offer clues as to how the world's disappearing coral can survive in changing oceans.

"The corals in the disturbed environments are the most pre-adapted and might be the most valuable in terms of saving them," said Andrew Baker, a marine biology professor at the University of Miami's Rosenstiel School of Marine and Atmospheric Science.